CATHODE

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to graphene-based porous carbon materials suitable for use as cathodes in lithium-sulfur batteries.

BACKGROUND OF THE DISCLOSURE

[0002] Increasing energy demands and environmental considerations have led to a search for more environmentally friendly energy storage systems that are safe, low cost, and that have high energy densities. Lithium-sulfur batteries are among the more promising energy storage devices and have attracted attention in recent years due to: (1) a high theoretical capacity of up to 1672 milliamp hour per gram (mAh/g), which is over 5 times that of currently used transition metal oxide cathode materials; (2) a relative low cost due to abundant resources of sulfur; and (3) the nonhazardous and environmentally benign nature of the components. The practical application of Li-S cells is still limited by several drawbacks, however, including: (1) the poor electrical conductivity of sulfur (5 10 ⁰ siemens per centimeter (S/cm)) limits the utilization efficiency of the active material and the rate capability; (2) the high solubility of polysulfide intermediates in the electrolyte results in a shuttling effect in the charge-discharge process; and (3) a large volumetric expansion (-80%) during charge and discharge results in rapid capacity decay and low Coulombic efficiency.

[0003] The high capacity and cycling ability of sulfur arises from the electrochemical cleavage and re-formation of sulfur-sulfur bonds in the cathode, which is believed to proceed in two steps. First, the reduction of sulfur to lithium higher polysulfides (LhSn, 4 < n < 8) is followed by further reduction to lithium lower polysulfides (LriSn, 1 < n < 3). The higher polysulfides are easily dissolved into the organic liquid electrolyte, enabling them to penetrate through the polymer separator and react with the lithium metal anode, leading to the loss of sulfur active materials. Even if some of the dissolved poly sulfides could diffuse back to the cathode during the recharge process, the sulfur particles formed on the surface of the cathode are electrochemically inactive owing to the poor conductivity. Such a degradation path leads to poor capacity retention, especially during long cycling (, more than 100 cycles).

[0004] In order to improve the capacity and improve the conductivity and prevent the polysulfide dissolution and shuttling, several different approaches have been developed during the past few decades. One strategy that has had success is the encapsulation of sulfur to prevent the leakage of active materials and suppress the shuttle effect of high order LriSn (L12S n, 4 < n < 8). A yolk-shell concept was proposed and demonstrated by Wei Seh el al. via sulfur at titanium dioxide (T1O2) yolk-shell nanoparticles which were proven as a superior cathode for Li-S batteries with excellent cycling stability. Wei Seh, Z. et al. , Sulphur-Ti02 yolk-shell nanoarchitecture with internal void space for long-cycle lithium-sulphur batteries, Nature Communications, 4, 1331 (2013). This group also developed an alternative approach to confine sulfur with voids in the form of hollow sulfur nanoparticles coated with a thin layer of polyvinylpyrrolidone that appeared promising. The sulfur-based yolk-shell nanostructure was further developed using a conducting polymer shell, polyaniline, and the cycling stability was demonstrated in Li-S batteries. Sulfur-carbon yolk-shell particles have also been synthesized with sulfur fully confined inside the conductive carbon shells, with the filling content of sulfur controlled and fine-tuned.

[0005] A second approach is the controllable deposition of the discharge product

L12S, which is an ionic and electronic insulator. Metal oxides have been used to trap poly sulfides to enhance cyclability of the Li-S battery via chemical adsorption. It has been reported that the composite cathode materials based on magnesium oxide/carbon MgO/C, lanthanum oxide/carbon La203/C and cerium(IV) oxide/carbon CeCh/C nanoflakes showed higher capacity and better cycling performance.

[0006] A third approach is to use dilithium sulfide L12S as a starting cathode material, which undergoes volumetric contraction instead of the expansion in the case of sulfur.

[0007] Each of these approaches, while demonstrating potential for incorporation into

Li-S batteries, has not fully overcome the drawbacks discussed herein.

[0008] These and other shortcomings are addressed by aspects of the present disclosure.

SUMMARY

[0009] Aspects of the disclosure relate to an electrically and thermally conductive graphene-sulfur composite material including: a porous graphene structure including a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material. [0010] In further aspects the disclosure relates to a method of making an electrically and thermally conductive graphene-sulfur composite material including a porous graphene structure including a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent and a sulfur material impregnated within the porous graphene structure. The method includes:

(a) obtaining a dispersion of graphene layers and an organic carbon-containing polymer in a solvent;

(b) drying the dispersion to obtain a porous graphene structure including a network of graphene layers and the organic carbon-containing polymer;

(c) annealing the porous graphene structure from step (b) to carbonize the organic carbon-containing polymer such that the graphene layers are attached to one another through the carbonized organic carbon-containing polymer; and

(d) combining the annealed porous graphene structure from step (c) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate the pores of and impregnate the annealed porous graphene structure.

[0011] In yet further aspects the disclosure relates to a lithium-sulfur battery including a cathode, an anode and an electrolyte, wherein the battery includes an electrically and thermally conductive graphene-sulfur composite material including: a porous graphene structure including a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

BRIEF DESCRIPTION OF THE FIGURES

[0012] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document.

[0013] FIG. 1 is a depiction of a graphene-sulfur composite material according to an aspect of the disclosure.

[0014] FIG. 2 is a process flow diagram illustrating a method for preparing a graphene-sulfur composite material according to an aspect of the disclosure.

[0015] FIG. 3A shows an image of a graphene-C foam. [0016] FIG. 3B shows a scanning electron microscope (SEM) image of the graphene-

C foam.

[0017] FIG. 4A shows an SEM image of S-graphene-C particles formed.

[0018] FIG. 4B shows an energy-dispersive X-ray (EDX) spectroscopy image of the sulfur-graphene composite.

[0019] FIG. 4C shows an x-ray powder diffraction spectrum of the sulfur-graphene-C composite.

[0020] FIG. 4D shows a thermogravimetric analysis of the sulfur-graphene-C composite.

DETAILED DESCRIPTION

[0021] The present disclosure can be understood more readily by reference to the following detailed description of the disclosure and the Examples included therein. In various aspects, the present disclosure pertains to an electrically and thermally conductive graphene- sulfur composite material including: a porous graphene structure including a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material. Methods of making the graphene-sulfur composite material, and a battery including the graphene-sulfur composite material, are also described. Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0022] Various combinations of elements of this disclosure are encompassed by this disclosure, e.g., combinations of elements from dependent claims that depend upon the same independent claim.

[0023] Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification.

[0024] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

Definitions

[0025] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term“comprising” can include the embodiments “consisting of’ and“consisting essentially of.” Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.

[0026] As used in the specification and the appended claims, the singular forms“a,”

“an” and“the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to“an organic polymer bridging agent” includes mixtures of two or more organic polymer bridging agents.

[0027] As used herein, the term“combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0028] Ranges can be expressed herein as from one value (first value) to another value (second value). When such a range is expressed, the range includes in some aspects one or both of the first value and the second value. Similarly, when values are expressed as approximations, by use of the antecedent‘about,’ it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. For example, if the value“10” is disclosed, then“about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed. [0029] As used herein, the terms“about” and“at or about” mean that the amount or value in question can be the designated value, approximately the designated value, or about the same as the designated value. It is generally understood, as used herein, that it is the nominal value indicated ± 10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is“about” or“approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0030] Disclosed are the components to be used to prepare the compositions of the disclosure as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively

contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C-E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the disclosure. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific aspect or combination of aspects of the methods of the disclosure. [0031] As used herein the terms“weight percent,”“wt%,” and“wt. %,” which can be used interchangeably, indicate the percent by weight of a given component based on the total weight of the composition, unless otherwise specified. That is, unless otherwise specified, all wt% values are based on the total weight of the composition. It should be understood that the sum of wt% values for all components in a disclosed composition or formulation are equal to 100

[0032] Unless otherwise stated to the contrary herein, all test standards are the most recent standard in effect at the time of filing this application.

[0033] Each of the materials disclosed herein are either commercially available and/or the methods for the production thereof are known to those of skill in the art.

[0034] It is understood that the compositions disclosed herein have certain functions.

Disclosed herein are certain structural requirements for performing the disclosed functions and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.

Graphene-Sulfur Composite

[0035] With reference to FIG. 1, aspects of the disclosure relate to a graphene-sulfur composite material (“composite material”) 100. The composite material 100 includes a porous graphene structure including a network of graphene layers 110 that are attached to one another through a carbonized organic polymer bridging agent 120. A sulfur material 130 is impregnated within the porous graphene structure. The graphene-sulfur composite material is electrically and/or thermally conductive in some aspects.

[0036] In further aspects the composite material includes only the porous graphene structure including a network of graphene layers 110 and a sulfur material 130 impregnated within the porous graphene structure. In other words, the organic polymer bridging agent 120 can be omitted in some aspects.

[0037] As used herein, the term“graphene” refers to a thin sheet of carbon atoms

(e.g., usually one-atom thick) arranged in a hexagonal format or a flat monolayer of carbon atoms that are tightly packed into a two dimensional 2-D honeycomb lattice (for example, sp2-bonded carbon atoms). Graphene does not include graphene oxide. In the context of the present disclosure,“graphene” also encompasses a stack of graphene sheets or monolayers (e.g., graphene stack having 2, 3, 4, 5, 6, 7, 8, 9, or 10, or more sheets or monolayers).

Graphene is commercially available from many sources. A non-limiting example of a source of graphene is Ningbo Morsh Tech. Co., Ltd., (China). [0038] The organic polymer bridging agent 120, if included, can attach between the graphene layers 110 such that the graphene layers 110 separate to form gaps or pores 115. Formation of pores 115 between graphene layers 110 provide space for the impregnated sulfur material 130 and may also provide electrically and/or thermally conductive pathways for electron transfer and/or heat dissipation in the final composite material. The pores 115 may also be located within the graphene layer 110 (not shown). In other words, the graphene layer 110 need not be a continuous layer of graphene; it can itself have gapes or pores 115. The composite material 100 can be, but is not limited to, a foam structure, a honeycomb structure, or a mesh structure. In one particular aspect, the composite material is a foam structure.

[0039] As shown, the sulfur material 130 can be impregnated in the graphene layers

110 and can fill or partially fill the pores 115. In some aspects (not shown), all pores 115 are filled with the sulfur material 130. The outer surface of the composite material can include sulfur material 130 on the surface of the graphene layers 110. The graphene layers 110 provide mechanical strength to the composite material 100.

[0040] In some aspects the graphene layers 110 may include other carbon-based materials, including but not limited to graphene oxide, carbon nanotubes (CNTs), carbon powder or a combination thereof. CNTs are nanometer-scale tubular-shaped graphene structures that have high specific surface area, excellent thermal conductivity, electrical conductivity, and excellent mechanical properties. CNTs have also been shown to be highly resistant to fatigue, radiation damage, and heat. Carbon nanotubes (CNTs) can have a variety of structural forms, including single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), triple-walled carbon nanotubes (TWNTs), multi-walled carbon nanotubes (MWNTs), graphenated carbon nanotubes (g-CNTs), nitrogen-doped carbon nanotubes (N-CNTs), or combinations thereof. CNTs are commercially available from many sources. A non-limiting example of a commercial source of MWCNTs is Shandong Dazhan Nanomaterials Co., Ltd., (China).

[0041] The sulfur material 130 can be provided from any suitable sulfur source.

Examples include, but are not limited to, elemental sulfur, lithium sulfide, lithium polysulfide or a combination thereof.

[0042] The organic polymer bridging agent 120 can help reduce or avoid the issues seen with coalescence of graphene layers and can aid in the formation of electrically and/or thermally conductive pores or channels throughout the porous graphene structure. [0043] The organic polymer bridging agent 120 can be any polymer that can attach to one or more of the graphene layers 110. Exemplary organic polymer bridging agents 120 include, but are not limited to, materials formed or derived from polyvinyl alcohol (PVOH), polyvinylpyrrolidone (PVP), starch, polyacrylonitrile (PAN), polydopamine (PDA), polyalkylene, polystyrene (PS), polyacrylate, polyester (PE), polycarbonate (PC), polyimide (PI), phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene (PE), polypropylene (PP), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene glycol (PEG), polypropylene glycol (PPG), glycogen, cellulose, or chitin, or any combination thereof. Of these polymers, at least PVOH, PVP, starch, phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, glycogen, cellulose, chitin, or any mixture thereof can be completely converted into amorphous carbon. In particular aspects the organic polymer bridging agent 120 is derived from polyvinyl alcohol (PVOH), polyvinylpyrrolidone (PVP), or starch.

[0044] In certain aspects the organic polymer bridging agent 120, if used, is carbonized such that at least 95%, at least 98%, or about 100% of the organic polymer bridging agent 120 is converted to carbon.

[0045] In some aspects the sulfur material is impregnated into the composite material

100 such that the sulfur material occupies at least 90 vol.% of the pores of the porous graphene structure. In further aspects the sulfur material occupies at least 95 vol.%, or at least 99%, or about 100% of the pores of the porous graphene structure.

[0046] The composite material 100 can in some aspects include from about 5 wt.% to about 20 wt.%, of the carbonized organic polymer bridging agent 120, based on the total weight of the porous graphene structure. In further aspects the composite material 100 includes from about 0 wt.% to about 20 wt.% of the carbonized organic polymer bridging agent 120, based on the total weight of the porous graphene structure (i.e., the organic polymer bridging agent 120 may be omitted in some aspects).

[0047] In certain aspects the composite material 100 includes from about 50 wt.% to about 95 wt.% of the sulfur material 130, based on the total weight of the graphene-sulfur composite material. In particular aspects the composite material 100 includes from about 55 wt.% to about 70 wt.% of the sulfur material 130, based on the total weight of the graphene- sulfur composite material.

[0048] As discussed above the composite material 100 may be in the form of, e.g., a foam structure, a honeycomb structure, or a mesh structure. In some aspects, the composite material 100 can be reduced in size (for example, macronized, micronized or nanosized), using known sizing methods (for example, granulation or powderification). In any of the above methods, the materials may be mixed together using suitable mixing equipment.

Examples of suitable mixing equipment include tumblers, stationary shells or troughs, Muller mixers (for example, batch type or continuous type), impact mixers, and any other generally known mixers, or generally known devices that can suitably provide dispersion of the graphene and the carbon nanotube. For solution chemistries, a mechanical stirrer, or sonifi cation can be used. Thus, in some aspects the composite material 100 is in granular or powder form.

[0049] The composite material may in some aspects be a three-dimensional (3-D) structure. In further aspects the composite material 100 may be a multi-dimensional (for example, 3, 4, 5, ... M dimensions) structure.

[0050] The composite material 100 may in some aspects be incorporated into a lithium-sulfur battery as described in more detail herein. In particular aspects the composite material 100 may be incorporated into a cathode of a lithium-sulfur battery.

Methods of Making a Graphene-Sulfur Composite

[0051] Aspects of the disclosure further relate to methods of making an electrically and thermally conductive graphene-sulfur composite material including a porous graphene structure including a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent and a sulfur material impregnated within the porous graphene structure. With reference to FIG. 2, the method 200 includes, at step 210, obtaining a dispersion of graphene layers 110 and an organic carbon-containing polymer in a solvent. At step 220, the dispersion is dried to obtain a porous graphene structure including a network of graphene layers 110 and the organic carbon-containing polymer. The porous graphene structure may be described as a graphene foam. At step 230, the porous graphene structure from step 220 is annealed to carbonize the organic carbon-containing polymer such that the graphene layers are attached to one another through the carbonized organic carbon- containing polymer (that is, the bridging agent 120). Annealing may be performed for cooling to room temperature at a rate of 1-20 °C/min. In further examples at step 230, the porous graphene structure from step 220 may be calcined. Calcining may be performed at a temperature from 400 °C to 1000 °C. At step 240, the annealed porous graphene structure from step 230 is combined with a sulfur material 130 under conditions sufficient to allow the sulfur material to infiltrate the pores 115 of and impregnate the annealed porous graphene structure. At step 240, the combining may proceed through a sulfur impregnation process.

The result is the composite material 100 described herein. [0052] As noted herein, in some aspects the composite material does not include the organic polymer bridging agent, and thus the step of annealing the porous graphene structure (step 230) may be omitted because there is no need to carbonize an organic carbon-containing polymer.

[0053] The graphene-sulfur composite material of the present disclosure can be prepared by processes known to those of ordinary skill in the art (for example, solution chemistry, sonication, annealing, lyophilization, curing, concentration, impregnation, or a combination thereof).

[0054] Step 210 of obtaining a dispersion of graphene layers 110 and an organic carbon-containing polymer in a solvent can be performed with any suitable solvent. In one aspects the solvent includes water, acetone, methanol, ethanol or a combination thereof. In a particular aspect the solvent is a mixed solvent including water and an organic solvent that is miscible with water and that has a surface tension lower than that of water, including but not limited to acetone, an alcohol such as methanol or ethanol, or any combination thereof. The dispersion can be mixed using known mixing methods for a time period sufficient to disperse the graphene and organic carbon-containing polymer (for example, ultrasonicated).

[0055] The ratio by volume of water to the organic solvent in the step 210 may be from about 1: 1 to about 20: 1 in some aspects. In certain aspects the ratio by volume of water to the organic solvent in the step 210 is from about 2: 1 to about 9: 1. The concentration of the graphene layers 110 in this step may be from about 2 milligram per milliliter (mg/mL) to about 20 mg/mL in some aspects. In particular aspects the concentration of the graphene layers 110 is from about 3 mg/mL to about 10 mg/mL.

[0056] In some aspects the dispersion of graphene layers 110 in step 210 further includes another carbon material, including but not limited to graphene oxide, carbon nanotubes, carbon powder or a combination thereof.

[0057] The sulfur material 130 introduced at step 240 may include, but is not limited to, elemental sulfur, lithium sulfide, lithium poly sulfide or a combination thereof.

[0058] The annealed porous graphene structure obtained at step 230 may be in any suitable form, including but not limited to a foam structure, a honeycomb structure, or a mesh structure.

[0059] The step of drying the dispersion to obtain a porous graphene structure including a network of graphene layers 110 and the organic carbon-containing polymer (step 220) may be performed at a temperature of from about 60 °C to about 85 °C in some aspects. In particular aspects the step may be performed at a temperature of from about 75 °C to about 80 °C. The dispersion can be placed in a drying chamber, which can have any length to diameter ratio. Exemplary ratios include 1.2: 1 to 3: 1, 1.3 to 2.5: 1, 1.5: 1 to 2.0: 1, or any ratio there between. In some aspects, the drying chamber is a blast-drying chamber. The drying step removes the solvent and assembles the graphene layers 110 and organic polymer bridging agent 120 into a porous graphene structure having a network of graphene layers 110 and organic polymer bridging agent 120 separating the graphene layers.

[0060] The step of annealing the porous graphene structure to carbonize the organic carbon-containing polymer such that the graphene layers are attached to one another through the carbonized organic carbon-containing polymer (step 230) may be performed at a temperature of from about 400 °C to about 1000 °C in some aspects. In particular aspects the step may be performed at a temperature of from about 400 °C to about 700 °C. By way of example, the dried sample can be removed from the drying chamber, and then placed in another vessel for annealing. In the annealing process, the porous graphene structure including the network of graphene layers 110 and the organic polymer bridging agent 120 is brought to a temperature sufficient to carbonize the organic polymer bridging agent, kept there for a time, and then cooled to room temperature (for example, 20 to 35 °C). During the annealing process, without wishing to be bound by theory, it is believed that carbonized organic polymer bridging agent 120 attaches graphene layers 110 to one another to form the graphene structure.

[0061] The step of combining the annealed porous graphene structure from step 230 with the sulfur material 130 under conditions sufficient to allow the sulfur material to infiltrate the pores 115 of and impregnate the annealed porous graphene structure (step 240) may be performed at a temperature of 140 °C to 500 °C in some aspects. In particular aspects the step may be performed at a temperature of from 150 °C to 160 °C.

[0062] As discussed above the composite material 100 may be in the form of, for example, a foam structure, a honeycomb structure, or a mesh structure. That structure may be further reduced in size as discussed above so that the composite material 100 is in granular or powder form.

[0063] The composite material 100 may in some aspects be incorporated into a lithium-sulfur battery as described in more detail herein. In particular aspects the composite material 100 may be incorporated into a cathode of a lithium-sulfur battery.

Lithium-Sulfur Battery Including Graphene-Sulfur Material

[0064] Aspects of the disclosure further relate to a lithium-sulfur battery including the graphene-sulfur composite material 100 described herein. The composite material 100 can individually include any of the features described herein and can be formed according to any of the methods described herein.

[0065] The lithium-sulfur battery includes in some aspects a cathode, an anode and an electrolyte. In certain aspects the cathode includes the composite material 100.

[0066] The resulting graphene-sulfur composite material provides the following advantages:

high electrical conductivity due to the graphene (and optional additional carbon materials (for example, graphene oxide, carbon nanotubes, carbon powder); and

the open-celled network facilitates impregnation of the sulfur material into the graphene structure.

[0067] Various combinations of elements of this disclosure are encompassed by this disclosure, for example, combinations of elements from dependent claims that depend upon the same independent claim.

Aspects of the Disclosure

[0068] In various aspects, the present disclosure pertains to and includes at least the following aspects.

[0069] Aspect 1A. An electrically and thermally conductive graphene-sulfur composite material comprising:

a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and

a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

[0070] Aspect 1B. An electrically and thermally conductive graphene-sulfur composite material consisting essentially of:

a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and

a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

[0071] Aspect 1C. An electrically and thermally conductive graphene-sulfur composite material consisting of:

a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and

a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material. [0072] Aspect 2. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-C, wherein the network of graphene layers further comprise graphene oxide, carbon nanotubes, carbon powder or a combination thereof.

[0073] Aspect 3. The electrically and thermally conductive graphene-sulfur composite material according to Aspect 1 A-C or 2, wherein the sulfur material comprises elemental sulfur, lithium sulfide, lithium polysulfide or a combination thereof.

[0074] Aspect 4. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-3, wherein the porous graphene structure comprises a foam structure, a honeycomb structure, or a mesh structure.

[0075] Aspect 5. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-4, wherein the organic polymer bridging agent is derived from polyvinyl alcohol (PVOH), polyvinylpyrrolidone (PVP), starch, polyacrylonitrile (PAN), polydopamine (PDA), polyalkylene, polystyrene (PS), polyacrylate, polyester (PE), polycarbonate (PC), polyimide (PI), phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene (PE), polypropylene (PP),

polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene glycol (PEG), polypropylene glycol (PPG), glycogen, cellulose, or chitin, or any combination thereof.

[0076] Aspect 6. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-5, wherein the carbonized organic polymer bridging agent is derived from polyvinyl alcohol (PVOH), polyvinylpyrrolidone (PVP), or starch.

[0077] Aspect 7. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-6, wherein the organic polymer bridging agent is carbonized such that at least 95% of the organic polymer bridging agent is converted to carbon.

[0078] Aspect 8. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-7, wherein the sulfur material occupies at least 90 vol.% of the pores of the porous graphene structure.

[0079] Aspect 9. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-8, comprising 5 wt.% to 20 wt.%, of the carbonized organic polymer bridging agent, based on the total weight of the porous graphene structure. [0080] Aspect 10. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-9, comprising 50 wt.% to 95 wt.%, of the sulfur material, based on the total weight of the graphene-sulfur composite material.

[0081] Aspect 11. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1A-10, wherein the graphene-sulfur composite material is in granular or powder form.

[0082] Aspect 12. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1 A-l 1, wherein the graphene-sulfur composite material is incorporated into a lithium-sulfur battery.

[0083] Aspect 13. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 1A-12, wherein the graphene-sulfur composite material is incorporated into a cathode of a lithium-sulfur battery.

[0084] Aspect 14 A. A method of making an electrically and thermally conductive graphene-sulfur composite material comprising a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent and a sulfur material impregnated within the porous graphene structure, the method comprising:

(a) obtaining a dispersion of graphene layers and an organic carbon-containing polymer in a solvent;

(b) drying the dispersion to obtain a porous graphene structure comprising a network of graphene layers and the organic carbon-containing polymer;

(c) annealing the porous graphene structure from step (b) to carbonize the organic carbon-containing polymer such that the graphene layers are attached to one another through the carbonized organic carbon-containing polymer; and

(d) combining the annealed porous graphene structure from step (c) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate the pores of and impregnate the annealed porous graphene structure.

[0085] Aspect 14B. A method of making an electrically and thermally conductive graphene-sulfur composite material comprising a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent and a sulfur material impregnated within the porous graphene structure, the method consisting of:

(a) obtaining a dispersion of graphene layers and an organic carbon-containing polymer in a solvent; (b) drying the dispersion to obtain a porous graphene structure comprising a network of graphene layers and the organic carbon-containing polymer;

(c) annealing the porous graphene structure from step (b) to carbonize the organic carbon-containing polymer such that the graphene layers are attached to one another through the carbonized organic carbon-containing polymer; and

(d) combining the annealed porous graphene structure from step (c) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate the pores of and impregnate the annealed porous graphene structure.

[0086] Aspect 14C. A method of making an electrically and thermally conductive graphene-sulfur composite material comprising a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent and a sulfur material impregnated within the porous graphene structure, the method consisting essentially of:

(a) obtaining a dispersion of graphene layers and an organic carbon-containing polymer in a solvent;

(b) drying the dispersion to obtain a porous graphene structure comprising a network of graphene layers and the organic carbon-containing polymer;

(c) annealing the porous graphene structure from step (b) to carbonize the organic carbon-containing polymer such that the graphene layers are attached to one another through the carbonized organic carbon-containing polymer; and

(d) combining the annealed porous graphene structure from step (c) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate the pores of and impregnate the annealed porous graphene structure.

[0087] Aspect 15. The method according to Aspect 14, wherein the solvent in step

(a) comprises water, acetone, ethanol, methanol or a combination thereof.

[0088] Aspect 16 A. The method according to Aspect 14A-C or 15, wherein a ratio by volume of water to the solvent in the dispersion in step (a) is 1 : 1 to 20: 1.

[0089] Aspect 16 A. The method according to Aspect 14A-C or 15, wherein a ratio by volume of water to the solvent in the dispersion in step (a) is 1 : 1 to 20: 1, wherein the solvent is an organic solvent.

[0090] Aspect 17. The method according to any of Aspects 14A-16B, wherein the concentration of the graphene layers in the dispersion in step (a) is 2 milligram per milliliter (mg/mL) to 20 mg/mL. [0091] Aspect 18. The method according to any of Aspects 14-17, wherein the dispersion of graphene layers further comprise graphene oxide, carbon nanotubes, carbon powder or a combination thereof.

[0092] Aspect 19. The method according to any of Aspects 14-18, wherein the sulfur material comprises elemental sulfur, lithium sulfide, lithium poly sulfide or a combination thereof.

[0093] Aspect 20. The method according to any of Aspects 14-19, wherein the annealed porous graphene structure comprises a foam structure, a honeycomb structure, or a mesh structure.

[0094] Aspect 21. The method according to any of Aspects 14-20, wherein the drying step (b) is performed at a temperature of 60 °C to 85 °C or the annealing step (c) is performed at a temperature of 400 °C to 1000 °C.

[0095] Aspect 22. The method according to any of Aspects 14-21, wherein the combining step (d) is performed at a temperature of 140 °C to 500 °C.

[0096] Aspect 23. The method according to any of Aspects 14-22, further comprising reducing the size of the graphene-sulfur composite material to granular or powder form.

[0097] Aspect 24. The method according to any of Aspects 14-23, further comprising incorporating the composite material into a lithium-sulfur battery.

[0098] Aspect 25. The method according to any of Aspects 14-24, further comprising incorporating the composite material into a cathode of a lithium-sulfur battery.

[0099] Aspect 26 A. A lithium-sulfur battery comprising a cathode, an anode and an electrolyte, wherein the battery comprises an electrically and thermally conductive graphene- sulfur composite material comprising:

a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and

a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

[00100] Aspect 26B. A lithium-sulfur battery comprising a cathode, an anode and an electrolyte, wherein the battery comprises an electrically and thermally conductive graphene- sulfur composite material consisting essentially of:

a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

[00101] Aspect 26C. A lithium-sulfur battery comprising a cathode, an anode and an electrolyte, wherein the battery comprises an electrically and thermally conductive graphene- sulfur composite material consisting of:

a porous graphene structure comprising a network of graphene layers that are attached to one another through a carbonized organic polymer bridging agent; and

a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

[00102] Aspect 27. The lithium sulfur-battery according to Aspect 26, wherein the cathode comprises the graphene-sulfur composite material.

[00103] Aspect 28. The lithium sulfur-battery according to Aspect 26 or 27, wherein the network of graphene layers further comprise graphene oxide, carbon nanotubes, carbon powder or a combination thereof.

[00104] Aspect 29. The lithium sulfur-battery according to any of Aspects 26-28, wherein the sulfur material comprises elemental sulfur, lithium sulfide, lithium poly sulfide or a combination thereof.

[00105] Aspect 30. The lithium sulfur-battery according to any of Aspects 26-29, wherein the porous graphene structure comprises a foam structure, a honeycomb structure, or a mesh structure.

[00106] Aspect 31. The lithium sulfur-battery according to any of Aspects 26-30, wherein the organic polymer bridging agent is derived from polyvinyl alcohol (PVOH), polyvinylpyrrolidone (PVP), starch, polyacrylonitrile (PAN), polydopamine (PDA), polyalkylene, polystyrene (PS), polyacrylate, polyester (PE), polycarbonate (PC), polyimide (PI), phenol formaldehyde resin, epoxy, polyalkylene glycol, polysaccharide, polyethylene (PE), polypropylene (PP), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene glycol (PEG), polypropylene glycol (PPG), glycogen, cellulose, or chitin, or any combination thereof.

[00107] Aspect 32. The lithium sulfur-battery according to any of Aspects 26-31, wherein the carbonized organic polymer bridging agent is derived from polyvinyl alcohol (PVOH), polyvinylpyrrolidone (PVP), or starch.

[00108] Aspect 33. The lithium sulfur-battery according to any of Aspects 26-32, wherein the organic polymer bridging agent is carbonized such that at least 95% of the organic polymer bridging agent is converted to carbon. [00109] Aspect 34. The lithium sulfur-battery according to any of Aspects 26-33, wherein the sulfur material occupies at least 90 vol.% of the pores of the porous graphene structure.

[00110] Aspect 35. The lithium sulfur-battery according to any of Aspects 26-34, comprising 5 wt.% to 20 wt.%, of the carbonized organic polymer bridging agent, based on the total weight of the porous graphene structure.

[00111] Aspect 36. The lithium sulfur-battery according to any of Aspects 26-35, comprising 50 wt.% to 95 wt.%, of the sulfur material, based on the total weight of the graphene-sulfur composite material.

[00112] Aspect 37. The lithium sulfur-battery according to any of Aspects 26-36, wherein the graphene-sulfur composite material is in granular or powder form.

[00113] Aspect 38: An electrically and thermally conductive graphene-sulfur composite material comprising:

a porous graphene structure comprising a network of graphene layers; and a sulfur material impregnated within the porous graphene structure to form the graphene-sulfur composite material.

[00114] Aspect 39. The electrically and thermally conductive graphene-sulfur composite material according to Aspect 38, wherein the network of graphene layers further comprise graphene oxide, carbon nanotubes, carbon powder or a combination thereof.

[00115] Aspect 40. The electrically and thermally conductive graphene-sulfur composite material according to Aspect 38 or 39, wherein the sulfur material comprises elemental sulfur, lithium sulfide, lithium polysulfide or a combination thereof.

[00116] Aspect 41. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 38-40, wherein the porous graphene structure comprises a foam structure, a honeycomb structure, or a mesh structure.

[00117] Aspect 42. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 38-41, wherein the sulfur material occupies at least 90 vol.% of the pores of the porous graphene structure.

[00118] Aspect 43. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 38-42, comprising 50 wt.% to 95 wt.%, of the sulfur material, based on the total weight of the graphene-sulfur composite material.

[00119] Aspect 44. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 38-43, wherein the graphene-sulfur composite material is in granular or powder form. [00120] Aspect 45. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 38-44, wherein the graphene-sulfur composite material is incorporated into a lithium-sulfur battery.

[00121] Aspect 46. The electrically and thermally conductive graphene-sulfur composite material according to any of Aspects 38-45, wherein the graphene-sulfur composite material is incorporated into a cathode of a lithium-sulfur battery.

[00122] Aspect 47 A. A method of making an electrically and thermally conductive graphene-sulfur composite material comprising a porous graphene structure comprising a network of graphene layers and a sulfur material impregnated within the porous graphene structure, the method comprising:

(a) obtaining a dispersion of graphene layers in a solvent;

(b) drying the dispersion to obtain a porous graphene structure; and

(c) combining the porous graphene structure from step (b) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate pores of and impregnate the porous graphene structure.

[00123] Aspect 47B. A method of making an electrically and thermally conductive graphene-sulfur composite material comprising a porous graphene structure comprising a network of graphene layers and a sulfur material impregnated within the porous graphene structure, the method consisting essentially of:

(a) obtaining a dispersion of graphene layers in a solvent;

(b) drying the dispersion to obtain a porous graphene structure; and

(c) combining the porous graphene structure from step (b) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate pores of and impregnate the porous graphene structure.

[00124] Aspect 47C. A method of making an electrically and thermally conductive graphene-sulfur composite material comprising a porous graphene structure comprising a network of graphene layers and a sulfur material impregnated within the porous graphene structure, the method consisting of:

(a) obtaining a dispersion of graphene layers in a solvent;

(b) drying the dispersion to obtain a porous graphene structure; and

(c) combining the porous graphene structure from step (b) with a sulfur material under conditions sufficient to allow the sulfur material to infiltrate pores of and impregnate the porous graphene structure. [00125] Aspect 48. The method according to Aspect 47, wherein the solvent in step

(a) comprises water, acetone, ethanol, methanol or a combination thereof.

[00126] Aspect 49. The method according to Aspect 47 or 48, wherein the ratio by volume of water to the organic solvent in the dispersion in step (a) is 1 : 1 to 20: 1.

[00127] Aspect 50. The method according to any of Aspects 47-49, wherein the concentration of the graphene layers in the dispersion in step (a) is 2 milligram per milliliter (mg/mL) to 20 mg/mL.

[00128] Aspect 51. The method according to any of Aspects 47-50, wherein the dispersion of graphene layers further comprise graphene oxide, carbon nanotubes, carbon powder or a combination thereof.

[00129] Aspect 52. The method according to any of Aspects 47-51, wherein the sulfur material comprises elemental sulfur, lithium sulfide, lithium poly sulfide or a combination thereof.

[00130] Aspect 53. The method according to any of Aspects 47-52, wherein the porous graphene structure comprises a foam structure, a honeycomb structure, or a mesh structure.

[00131] Aspect 54. The method according to any of Aspects 47-53, wherein the drying step (b) is performed at a temperature of 60 °C to 85 °C.

[00132] Aspect 55. The method according to any of Aspects 47-54, wherein the combining step (c) is performed at a temperature of 140 °C to 500 °C.

[00133] Aspect 56. The method according to any of Aspects 47-55, further comprising reducing the size of the graphene-sulfur composite material to granular or powder form.

[00134] Aspect 57. The method according to any of Aspects 47-56, further comprising incorporating the composite material into a lithium-sulfur battery.

[00135] Aspect 58. The method according to any of Aspects 47-57, further comprising incorporating the composite material into a cathode of a lithium-sulfur battery.

EXAMPLES

[00136] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric. Unless indicated otherwise, percentages referring to composition are in terms of wt%.

[00137] There are numerous variations and combinations of reaction conditions, e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures and other reaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.

[00138] Polyvinylpyrrolidone (PVP, Mw=55,000) and sulfur was purchased from Sigma- Aldrich. Graphene was obtained from Ningbo Morsh Inc. All solvents were used as received without further purification.

[00139] Scanning electron microscopic (SEM) images were taken by a Nova

NanoSEM (FEI). Energy dispersive x-ray spectroscopy (EDX) was obtained using a Nova NanoSEM (FEI) operated at 10 kilovolts (kV). X-ray diffraction (XRD) patterns were recorded at room temperature on a powder PANalytical Empyrean diffractometer using CuKa radiation (l = 1.54059 A) at 40 kV and 40 milliamps (mA). Thermogravimetric analysis (TGA) was obtained using a TGA Q500 (TA instrument) from 25 - 800 °C with a heat ramp of 20 °C/min under nitrogen atmosphere.

Preparation of 3-D graphene-carbon linked foam (Graphene-C foam)

[00140] Graphene (2 g) and PVP (2 g) were dispersed in 500 ml of ethanol/water ( 4: 1 in v/v) mixture by sonication to obtain a homogeneously graphene suspension. The suspension was then placed in an oven and dried at 80 °C for 72 hours to obtain the 3-D graphene-PVP foam. The 3-D graphene-PVP foam was annealed in an oven at 5 °C/min to 500 °C and held for 2 hours to carbonize the polymer PVP and a graphene-carbon (graphene- C) foam was obtained. FIG. 3A shows the graphene-C foam and FIG. 3B shows a SEM image of the graphene-C foam. As apparent from FIGS. 3A and 3B, macropores were formed in the foam.

Preparation of sulfur-graphene Composite (S-graphene-C):

[00141] An amount of 1 g of Graphene@C foam and 10 g of sulfur powder were heated at 200 °C overnight and then kept under vacuum to impregnate melted sulfur into the pores of the foam. Simultaneously, the extra sulfur on the surface of foam was removed by sublimation. After cooled down to room temperature, the obtained composite was ground to small powder.

[00142] FIG. 4A shows an SEM image of the S-graphene-C particles formed. FIG.

4B shows an energy-dispersive X-ray (EDX) spectroscopy of the composite. CK, OK, and SK, refer to carbon, oxygen, and sulfur with K as an electron Shell/orbital to which an outer- shell/orbit electrons, with higher energy, transfers following excitation/ejection of the inner- shell electron. Weight percent is Wt% and At% is the atom percent which describes the abundance of number of atoms of one element relevant to the total number of atoms detected in the spectrum. As shown, the EDX pattern shows the obtained composite has carbon and sulfur elements. X-ray powder diffraction (XRD) patterns of sulfur, graphene-C foam, and S- graphene-C are apparent in FIG. 4C. For the XRD of S-graphene-C, a wide shoulder peak at around 26.3° is attributed to peak of graphene. Results for thermogravimetric analysis are presented in FIG. 4D. The TGA of the obtained composite indicates the sulfur loading of S- graphene-C is about 85%.

[00143] While typical aspects have been set forth for the purpose of illustration, the foregoing descriptions should not be deemed to be a limitation on the scope herein.

Accordingly, various modifications, adaptations, and alternatives can occur to one skilled in the art without departing from the spirit and scope herein.

[00144] It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

[00145] The patentable scope of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[00146] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other aspects can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may he in less than all features of a particular disclosed aspect. Thus, the following claims are hereby incorporated into the Detailed Description as examples or aspects, with each claim standing on its own as a separate aspect, and it is contemplated that such aspects can be combined with each other in various combinations or permutations. The scope of the disclosure should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.